(1) Field of the Invention
The present invention relates to an image forming unit that is demountably mounted to an electrophotographic image forming apparatus, and in particular to an image forming unit including a mechanism for collecting and reusing residual toner after transfer, and an image forming apparatus including the image forming unit.
(2) Description of the Related Art
In general, in an electrophotographic image forming apparatus such as a copying machine and a printer, image formation is performed in the following manner. A developer supplies toner to an electrostatic latent image formed on an image carrier such as a photoreceptor drum to develop the electrostatic latent image. The developed toner image is transferred onto a recording sheet and thermally fixed to the recording sheet.
In the transfer, not all of the toner on the image carrier is transferred onto the recording sheet, and a part of the toner remains on a surface of the image carrier. Therefore, prior to a next image forming process, it is necessary to remove residual toner that remains on the surface of the image carrier after transfer. There have been known various methods to remove the residual toner. A method widely used is to scrape the image carrier, and collect the residual toner by having a plate-shaped elastic blade in sliding contact with the surface of the image carrier, because this method is easy and inexpensive.
Conventionally, the collected residual toner has been discarded as waste toner. However, in recent years, in order to effectively utilize resources out of concern for environmental problems, the collected residual toner is conveyed to a developer apparatus or a toner supply apparatus for reuse (recycle) in some image forming apparatuses. The conveyed residual toner is mixed with fresh toner that is discharged from a toner container such as a toner bottle, and used for developing an electrostatic latent image.
Japanese Patent Application Publication No. H8-286513 (hereinafter, Patent Document 1) discloses a toner recycling apparatus that is composed of a fresh toner conveyer and a recycled toner conveyer, and has a mechanism for mixing fresh toner and recycled toner that are each conveyed by the above conveyers and supplying the mixed toner to a developing apparatus.
The recycled toner has been damaged in an image forming process, as surface preparation agents has been buried or detached. Therefore, unfortunately, flowability of the recycled toner is greatly decreased compared to flowability of the fresh toner.
However, with a structure of Patent Document 1, the fresh toner conveyer and the recycled toner conveyer are each disposed horizontally and there is no mechanism for making the recycled toner flow more easily. Therefore, there is a problem that the recycled toner adheres to a screw of the toner conveyer or an inner wall of a pipe and accordingly a toner clogging is likely to occur in a toner conveying passage.
Additionally, the Patent Document 1 discloses a two-axis configuration in which the fresh toner conveyer and the recycled toner conveyer have a respective screw. The fresh toner conveyer and the recycled toner conveyer are each independently driven/controlled by a respective drive source. That would cause an increase in cost and size of the apparatus.